In today's computers, cursor movement, to select window and menu items, is often controlled using input devices such as mice or trackballs. Mice and trackballs both include a housing partially enclosing a rotatable ball and have one or more depressable buttons. Electronic encoders sense the rotation of the ball and generate signals indicating the ball's rotation. These signals are used to control movement of a cursor on a display screen of the computer. The ball either protrudes from the top of the housing (in a trackball) or below the housing (in a mouse). With a mouse, the housing is moved across a surface, typically a table top, causing the ball protruding below the housing to roll in a similar direction. The electronic encoders produce signals that are output to a computer reflecting such movement.
The buttons are used to enter commands into the computer, usually based on the current position of the cursor on the display screen. Depressing the button permits the user to enter various commands into the computer. Examples of such commands include: opening or pulling down a menu; launching an application; create starting, ending or other points in a graphic pattern on the screen; moving objects to different locations on the screen; and the like.
Currently commercially available computer input devices generally permit only two-dimensional positioning of a cursor. Some computer program applications are available which permit illusory positioning of a cursor in three-dimensional space on a two-dimensional video display device. European Patent Application WO 93/11526 describes a computer input device which permits three-dimensional positioning of a cursor. This device uses a stationary transmitter and a moveable receiver. The transmitter includes three speakers spaced apart in an "L" or "T" shape. The movable receiver includes three microphones spaced apart in a triangular shape. The speakers transmit ultrasonic signals which are received by the microphones. A calibration microphone is further included on the receiver. Control circuitry measures the time of delay for sound to travel from each of the three speakers in the transmitter to each of the three microphones in the receiver. From this delay information and the speed of sound in air (calibrated for that time and location), the device determines the three-dimensional position of the movable receiver with respect to the stationary transmitter. Sophisticated electronics and expensive components are required in this three-dimensional computer input device to perform the position/attitude computations.
Overall, the inventors are unaware of any three-dimensional cursor positioning or computer input device which avoids sophisticated electronics and expensive components yet provides accurate cursor positioning.